Selectively activated shape memory device

ABSTRACT

A shape memory device includes a shape memory alloy member configured to have at least a portion of the shape memory alloy member be selectively activated. A heating device is coupled to the member and configured to provide heat to a selected section of the member and activate at least a portion of the selected section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This invention is a continuation-in-part of U.S. patent application Ser.No. 08/708,586, filed Sep. 5, 1996, entitled "DISTRIBUTED ACTIVATOR FORA TWO-DIMENSIONAL SHAPE MEMORY ALLOY", incorporated herein by reference.

BACKGROUND

1. Field of the Invention

This application relates to shape memory devices, and more particularlyto a spatially addressable shape memory device.

2. Description of Related Art

Materials which change their shape in response to external physicalparameters are known and appreciated in many areas of technology. Shapememory alloys (hereafter "SMA") is a material that undergoes amicro-structural transformation from a martensitic phase at a lowtemperature to an austenitic phase at a high temperature. In themartensitic phase an SMA exhibits low stiffness and may be readilydeformed up to 8% total strain in any direction without adverselyaffecting its memory properties. When heated to an activationtemperature, the SMA becomes two to three times stiffer as it approachesits austenitic state. At the higher temperature, the SMA attempts toreorganize itself on the atomic level to accommodate a previouslyimprinted or "memorized" shape. When the SMA cools it returns to itssoft martensitic state.

A shape may be trained into an SMA by heating it well beyond itsactivation temperature to its annealing temperature and holding it therefor a period of time. For a TiNi SMA system, the annealing programconsists of geometrically constraining the specimen, and heating it toapproximately 520 degrees C. for fifteen minutes. Usually, functionallyis enhanced by leaving in a certain amount of cold working byabbreviating the anneal cycle.

U.S. Pat. No. 4,543,090 (hereafter the "'090 Patent") discloses acatheter with two distinct SMA actuators. One actuator assumes apredetermined shape when heated to a predetermined temperature. The twoactuators are coupled to each other with a coupling device so that whenone of the actuator moves to its predetermined shape a force is appliedto move the second actuator in the direction of the first actuator. Eachactuator is only able to move to a single predetermined shape. Theactuators do not include a heating device with at least twomicro-fabricated address lines. The limitations of the '090 Patent arealso found in U.S. Pat. No. 4,601,705.

It would be desirable to provide a shape memory alloy device that has asheet of shape memory alloy where a section of the sheet can beselectably activated.

SUMMARY

An object of the present invention is to provide a shape memory devicethat is selectably activated.

Another object of the present invention is to provide a shape memorydevice that is activated to more than a single predetermined shape.

Still another object of the present invention is to provide a shapememory device with a shape memory alloy and a heating device thatincludes at least one micro-fabricated conductive path.

Another object of the present invention is to provide a shape memorydevice where an activation of at least a portion of the shape memorydevice provides a variable Young's modulus of at least a portion of theshape memory device.

Yet another object of the present invention is to provide a medicaldevice that includes a shape memory alloy actuator that is selectablyactivated to a selected site of the actuator.

Still a further object of the present invention is to provide a medicaldevice that includes a sheet of shape memory alloy that is activated ata selected site of the sheet and the sheet is coupled to a catheterbody.

Another object of the present invention is to provide a medical devicewith a single shape memory alloy actuator.

A further object of the present invention is to provide a shape memorydevice with a plurality of independently addressable actuators.

Yet a further object of the present invention is to provide a thermallyactivated apparatus that includes a temperature-activated actuatorconfigured to move to a plurality of different predetermined shapes.

These and other objects of the invention are achieved in a shape memorydevice that includes a shape memory alloy member configured to have atleast a portion of the shape memory alloy member be selectivelyactivated. A heating device is coupled to the member and configured toprovide heat to a selected section of the member and activate at least aportion of the selected section.

In one embodiment of the invention, a shape memory device includes asheet of a shape memory alloy. The sheet is selectably activated to aselected site of the sheet and includes at least two independentlyactuateable elongated members. A heating device is positioned adjacentto or on a surface of the sheet to provide heat to a selected section ofthe sheet and create a bending force within at least a portion of theselected section. The heating device includes at least onemicro-fabricated conductive path.

In another embodiment of the invention, a medical device includes anelongated device at least partially made of a shape memory alloy memberconfigured to be selectably activated at a selected site of the member.A heating device is coupled to the member and configured to provide heatto a selected section of the member and activate at least a portion ofthe selected section.

In yet another embodiment of the invention, a catheter is provided withan elongated device that includes a distal end and proximal end. A shapememory alloy member is configured to be selectably activated at aselected site of the member. The member is coupled to the elongateddevice. A heating device is coupled to the member and configured toprovide heat to a selected section of the member and activate at least aportion of the selected section.

In still another embodiment of the invention, a shape memory deviceincludes a shape memory alloy member that is configured to be selectablyactivated at a selected site of the member. The member has at least twoindependently activated elongated portions. A heating device is coupledto the member and configured to provide heat to a selected section ofthe member and activate at least a portion of the selected section.

In another embodiment of the invention, a thermally activated apparatusincludes a temperature-activated actuator. The actuator is configured tomove to a plurality of predetermined shapes. A heating device isconfigured to deliver thermal energy to at least a selected portion ofthe actuator.

In still a further embodiment of the invention, a medical deviceincludes an elongated member with a proximal portion and a distalportion configured to be inserted into a body. An electrically-activatedactuator is coupled to the elongated member. The actuator is configuredto move to a plurality of predetermined shapes. An electrical energysource is coupled to the electrically-activated actuator and configuredto deliver energy to at least a selected portion of the actuator.

In yet another embodiment of the invention, a thermally activatedapparatus includes an electrically-activated actuator coupled to anelongated member. The actuator is configured to move to a plurality ofpredetermined shapes. An electrical energy source is coupled to theelectrically-activated actuator and configured to deliver energy to atleast a selected portion of the actuator.

In various embodiments of the invention, an activation of at least aportion of the selected section of the actuator provides a variableYoung's modulus of at least a portion of the actuator. The heatingdevice can include a micro-fabricated conductive path. The actuator canbe made of a continuous sheet of a shape memory alloy, a sheet of ashape memory alloy which includes perforations, or a plurality ofinterconnected separate shape memory alloy actuators. The actuator canhave a three-dimensional geometry, a wire-like geometry, a tube-likestructure and the like. A micro-fabricated circuit, a micro-fabricatedsensor, or a micro-fabricated transducer can be coupled to the heatingdevice.

The medical device of the present invention can be an endoscope, acatheter, a cannula, an introducer, a laparoscope, a trocar and acatheter. The operation mode of the shape memory alloy of the medicaldevice is achieved by, (i) one-way shape memory effect acting on anelastic body such as a catheter which provides a return force, (ii)using one-way shape memory effect and directly applying a restoringforce with a superelastic shape memory alloy spring, an elastomericspring and the like, or (iii) utilizing a two-way shape memory effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a deactivated two-dimensional sheetaccording to the invention.

FIG. 2 is a perspective view of the two-dimensional sheet of FIG. 1illustrating micro-fabricated structures.

FIG. 3 is an isometric view of the two-dimensional sheet of FIG. 1 inthe activated state.

FIG. 4 is an isometric view of a portion of the two-dimensional sheet ofFIG. 1.

FIG. 4(a) is a cross section of the portion of the two-dimensional ofFIG. 4.

FIG. 4(b) is a graph of the temperature distribution in the portion ofFIG. 4(a).

FIG. 5 is a hysterisis curve of the transition between the martensiticand austenitic states as a function of temperature.

FIG. 6 is a cross section of a two-dimensional sheet with an insulatinglayer and a coating layer.

FIG. 7 is a cross section of a two-dimensional sheet with point-wiseapplied insulating layer and a coating layer.

FIG. 8 is a cross section of a two-dimensional sheet with a coatinglayer.

FIG. 9 is an exploded view illustrating the assembly of atwo-dimensional sheet and the activation elements according to theinvention.

FIG. 10 is a diagram showing the equivalent circuit of the activationmechanism.

FIG. 11 is a side view illustrating the deflection of a two-dimensionalsheet according to the invention.

FIG. 12 is a perspective view illustrating a complex pre-trained shapeof a sheet according to an aspect of the invention.

FIG. 13 is a diagram showing the equivalent circuit of an embodimentusing deflection sensors.

FIG. 14 is a cross sectional view of a two-dimensional sheet withdeflection sensors.

FIG. 15 is a cross sectional view of a two-dimensional sheet withdeflection sensors mounted next to heating elements.

FIG. 16 is a cross sectional view showing a two-dimensional sheet with atemperature sensor.

FIG. 17 is a cross sectional view of a two-dimensional sheet withprotective coating applied over the eating elements.

FIG. 18 is a cross section of a two-dimensional sheet using vanes forheat dissipation.

FIG. 19 is a cross section of a two-dimensional sheet using water ductsfor heat dissipation.

FIG. 20 is a cross section of a catheter with the actuator illustratedin FIG. 2.

FIG. 21 is a cross section view of two actuators illustrated in FIG. 2with a thermally insulating elastomer.

FIG. 22 illustrates the actuator of FIG. 2 coupled to a catheter.

FIG. 23 illustrates an actuation path of the actuator of FIG. 2 in apush embodiment.

FIG. 24(a) is a perspective view of an actuator of the present inventioncoupled to the distal end of a catheter and the actuator includesactuator slots that extending to a distal end of the actuator.

FIG. 24(b) is a perspective view of an actuator of the present inventionwith the distal ends of "finger-like segments" of actuator 12 joined tothe distal end of a catheter.

FIG. 24(c) is a perspective view of an actuator of the present inventioncoupled to a distal end of a catheter and the actuator includes slotsthat do not extend to proximal or distal ends of the actuator.

FIG. 25 illustrates the positioning of the actuator of FIG. 2 in aninterior of a catheter.

FIG. 26 illustrates the inclusion of the actuator of FIG. 2 in acatheter body.

FIG. 27 illustrates the selective heating capability of the actuator ofFIG. 2.

FIG. 28 is a cross section of an a catheter without a lumen and theactuator of FIG. 2 positioned in the catheter.

FIG. 29 is a perspective view of a mesh configuration of the actuator ofthe present invention.

FIG. 30 illustrates the actuator of FIG. 29 coupled to a catheter.

FIG. 31 illustrates the result of applying heat to selected sections ofthe mesh of FIG. 30.

FIG. 32 illustrates a shape memory alloy corrugated tube.

FIG. 33 illustrates the result of applying heat to selected sections ofthe corrugated tube of FIG. 32.

FIG. 34 illustrates a cross-sectional view of the apparatus of FIG. 32.

DESCRIPTION

One embodiment of the present invention is a shape memory device thatincludes a shape memory alloy member configured to have at least aportion of the shape memory alloy member selectively activated. Aheating device is coupled to the member and configured to provide heatto a selected section of the member and activate at least a portion ofthe selected section.

In another embodiment of the present invention, a shape memory deviceincludes a sheet of a shape memory alloy. The sheet is selectablyactivated to a selected site of the sheet and includes at least twoindependently actuateable elongated members. A heating device ispositioned adjacent to or on a surface of the sheet to provide heat to aselected section of the sheet and create a bending force within at leasta portion of the selected section. The heating device includes at leastone micro-fabricated conductive path.

In still another embodiment of the invention, a medical device includesan elongated device at least partially made of a shape memory alloymember configured to be selectably activated at a selected site of themember. A heating device is coupled to the member and configured toprovide heat to a selected section of the member and activate at least aportion of the selected section.

In yet another embodiment of the invention, a medical device is anelongated device that includes a distal end and proximal end. A shapememory alloy member is configured to be selectably activated at aselected site of the member. The member is coupled to the elongateddevice. A heating device is coupled to the member and configured toprovide heat to a selected section of the member and activate at least aportion of the selected section.

In still another embodiment of the invention, a shape memory deviceincludes a shape memory alloy member that is configured to be selectablyactivated at a selected site of the member. The member has at least twoindependently activated elongated portions. A heating device is coupledto the member and configured to provide heat to a selected section ofthe member and activate at least a portion of the selected section.

In another embodiment of the invention, a thermally activated apparatusincludes a temperature-activated actuator. The actuator is configured tomove to a plurality of predetermined shapes. A heating device isconfigured to deliver thermal energy to at least a selected portion ofthe actuator.

In still a further embodiment of the invention, a medical deviceincludes an elongated member with a proximal portion and a distalportion configured to be inserted into a body. An electrically-activatedactuator is coupled to the elongated member. The actuator is configuredto move to a plurality of predetermined shapes. An electrical energysource is configured to be coupled to the electrically-activatedactuator and deliver energy to at least a selected portion of theactuator.

In yet another embodiment of the invention, a thermally activatedapparatus includes an electrically-activated actuator coupled to anelongated member. The actuator is configured to move to a plurality ofpredetermined shapes. An electrical energy source is coupled to theelectrically-activated actuator and configured to deliver energy to atleast a selected portion of the actuator.

In various embodiments of the invention, an activation of at least aportion of the selected section of the actuator provides a variableYoung's modulus of at least a portion of the actuator. The heatingdevice can include a micro-fabricated conductive path. The actuator canbe made of a continuous sheet of a shape memory alloy, a sheet of ashape memory alloy which includes perforations, or a plurality ofinterconnected separate shape memory alloy actuators. The actuator canhave a three-dimensional geometry, a wire-like geometry, a tube-likestructure and the like. A micro-fabricated circuit, a micro-fabricatedsensor, or a micro-fabricated transducer can be coupled to the heatingdevice.

The medical device of the present invention can be an endoscope, acatheter, a cannula, an introducer, a laparoscope, a trocar, surgicalintervention devices and the like. The operation mode of the shapememory alloy device is achieved by, (i) one-way shape memory effectacting on an elastic body such as a catheter which provides a returnforce, (ii) using one-way shape memory effect and directly applying arestoring force with a superelastic shape memory alloy spring, anelastomeric spring and the like, or (iii) utilizing a two-way shapememory effect.

Referring now to FIG. 1, a shape memory device 10 includes a sheet of ashape memory alloy 12 that is made entirely of a SMA. Most commonexamples include TiNi alloys and CuZnAl alloys. Other alloys and shapememory polymers can also be used. The ratio of the thickness of sheet 12to the lateral extent of a heating element 14 should be preferably assmall as possible, while still capable of maintaining the integrity ofsheet 12. Shaped memory device 10 is configured to be selectablyactivated to a selected site of sheet 12. This provides for themovement, or actuation, of different sections of sheet 12. By heatingportions of sheet 12, spatially complex bending forces are generatedwithin sheet 12. Heating elements 14 provide thermal energy to sheet 12directly, ohmicaly, and from a number of different energy sourcesincluding but not limited to electromagnetic, microwave, resistiveheating, ultrasound and RF. Heating elements 14 are electricallyisolated from sheet 12, from each other and from the local environment.

SMA sheet 12 can be flexible and produced by a variety of commonmachining methods; such as rolling of thin foils from wire or thin platestock, sectioning thin wafers from bar stock, or like methods. Wafers ofSMA material may be sliced from bar stock using a conventional band saw,a cold saw, an annular diamond wet saw, or electro-discharge machining(EDM) or like methods. The resulting wafers or foils can be heat treatedto a flat condition and precision-ground to any desired thickness. SMAbulk properties are assured as the material is obtained directly frombulk. The SMA material contained in sheet 12 can be thermallypre-trained prior to assembly or left untrained. The choice depends onthe eventual application.

A plurality of heating elements 14 are positioned on top of SMA sheet 12and insulated from sheet 12 by an electrically insulating layer 16. Itis most convenient to laminate or otherwise deposit electricallyinsulating layer 16 on sheet 12. Electrically insulating layer 16prevents current leakage between heating elements 14 and electricallyconducting sheet 12. Electrically insulating layer 16 is also preferablyis a good thermal conductor. Preferred insulating materials includepolyimide elastomers, plastics, silicon nitride Si_(x) N_(y), and thelike. The thickness of electrically insulating layer 16 should be smallin relation to its lateral extent. For example, electrically insulatinglayer 16 may be a 2000 Å silicon nitride layer to ensure adequatethermal coupling, and to ensure thermal conductivity between heatingelements 14 and sheet 12.

In the embodiment of FIG. 1, heating elements 14 are in the form of thinfilm resistors. Most preferably, heating elements 14 are ohmic heatersor other similar devices capable of converting electrical current tothermal energy. They can be comprised of any conventional resistivematerial such as TiW or TaO. Conveniently, the resistive material isfirst deposited and patterned on layer 16 by well known VLSI ormicro-machining techniques. Heating elements 14 are patterned orotherwise formed according to well-known photolithographic proceduressuch as the additive process of lift off or the subtractive process ofdry or wet etching.

Shape memory device 10 can be operated in either open loop or closedloop mode. In open loop mode, a predetermined path of travel isprogrammed in a microprocessor. The microprocessor then provides outputsignals to the address decode circuitry which is integrated in VLSI on aproximal portion of shape memory device 10. The predetermined travelpath is then mapped into latch registers or logic gates in the addressdecode circuitry in accordance with techniques which are well known. Theaddress decode circuitry then activates selected portions of shapememory device 10.

In the closed loop mode, the position signal received from each positionor bend sensor is utilized by an adaptive feedback control method thatcenters shape memory device 10 on a path of travel. The microprocessoris able to determine the angular displacement and thus the position ofshape memory device 10. From this, the overall position of shape memorydevice 10 can be determined for given positional intervals.

Angular displacement of shape memory device 10 may also be determined byobserving the current and/or voltage delivered to each heater element14. From the current and voltage information an instantaneous localresistance may be inferred. Conventional means are provided for sensingthe voltages at different nodes. The voltage information is provided tomicroprocessor over a communication path.

A look-up table of temperature/resistance relationships is embodied inthe microprocessor. The look-up table is optimized for each shape memorydevice 10 formulation in order to provide a narrow hysterisis loop. Inthe look-up table, the microprocessor then correlates each resistancevalue with a temperature and consequently can determine the activationstate and thus, the angular displacement and position of shape memorydevice 10. A position mapping means in the microprocessor comprises ameans for establishing a reference array comprising a locus of angularpositions for shape memory device 10. This in turn defines a path oftravel for shape memory device 10. Once a locus of angular positions isstored, the memorized travel path is repeatable with extreme speed.Accordingly a catheter coupled to shape memory device 10 can instantlyreverse both its direction and activation sequence so that it preciselyretraces even the most complex path of travel. The position mappingmeans may store one or more paths of travel in memory.

As shown in FIG. 2, heating elements 14 may include at least onemicro-fabricated conductive path 18 coupled to a single current source.A single current source can deliver current to any number of differentheating elements 14 by the use of multiplexing power transistors. Atransistor may be pulse width modulated to deliver a metered amount ofpower. Optionally included are a micro-fabricated circuit 20, amicro-fabricated sensor 22 and a micro-fabricated transducer 24.Micro-fabricated sensors include but are not limited to pressure,temperature, electrosonic, voltage potential, chemical, chemicalpotential and an electromagnetic sensor. Micro-fabricated transducersinclude temperature, electrosonic, voltage potential and anelectro-magnetic transducer. FIG. 3 shows a particular case wherein sixheating elements 14, labeled as 14A-14F, are providing heat. In the casewhere shaped memory device 10 is limitedly constrained by itsenvironment heat traverses section 16A-16F of insulating layer 16 andcauses adjacent portions 12A-12F of SMA sheet 12 to reach activationthreshold. As a result, portions of 12A-12F are activated and assume awell-defined shape and in the process provide useful activation forces.As shown, the local deformation is upward convex. Once portions 12A-12Fconvert to a predominantly austenitic composition and assume theirpre-determined shapes, the areas of sheet 12 surrounding those portionsare characterized by martensitic composition and deform in accordancewith conventional laws of continium mechanics. In the simple case ofFIG. 3, the remainder of sheet 12 remains flat or otherwise undisturbedfrom its initial state.

In FIG. 4 the thickness of sheet 12 is labeled by S. For clarity, aparticular heating element 14X has been selected to explain the detailsof the invention. Heating element 14X has associated with it an adjacentportion 12X of sheet 12. As shown, heating element 14X has associatedwith it a section 16X of electrically insulating layer 16 as well.Portion 12X is located directly underneath heating element 14X. Thewidth of portion 12X is denoted by D. As shown, heating element 14Xprovides heat to portion 12X exclusively. Heat propagates throughsection 16X and into section 12X which represents a localized portion ofsheet 12.

The principles behind the heating process and the shape assumed byadjacent portions 12 are best illustrated in FIG. 4A with a singleheating element 14X. For clarity, the predetermined shape assumed byadjacent portion 12X upon heating has not been shown. The heat generatedby element 14X, whose width is indicated by W, passes along arrowsthrough insulating layer 16. In particular, the thermal energy traversessection 16X of layer 16. Layer 16 is proportionally very thin comparedto the lateral dimensions, and thus section 16X readily transfers theheat to sheet 12. Once in sheet 12 the heat propagates throughoutadjacent portion 12X. Due to a relatively thin section S heat conductivein the lateral direction is far less than in the normal direction.During a typical operation cycle the applied heat energy remainslocalized.

Graph 4B represents temperature distributions at an arbitrary fixeddepth below heater 14X. The graph in FIG. 4B shows the temperaturedistribution laterally, in the X direction, inside portion 12X. Directlyunder element 14X the temperature remains at a maximum, as indicated bythe flat portion of the curve from -W/2 to +W/2. In other words, theheat delivered to portion 12X does not propagate to other portions 12,e.g., portion 12Y. Instead, the heat radiates along arrows R out ofsheet 12 before reaching other portions 12.

As already mentioned, the shape of adjacent portions 12 depends on thepre-trained shape of the SMA or sheet 12 in those regions. Also, theshape depends on the temperature maintained in portions 12. Fullconformity to the pre-trained shape is achieved when the temperature inportions 12 is equal or higher than the critical temperature at whichthe SMA material attains the austenitic state. This is best shown in thegraph of FIG. 5. At temperatures below T₁ the SMA material remainspliable, as dictated by the martensitic properties. Therefore, portions12 maintained at or below T₁ will conform to the shape imparted to themby the surroundings. The transition to the austenitic state occursbetween temperatures T₁ and T₂. When portions 12 are kept in thistemperature range they will assume an intermediate shape between therelaxed and pre-trained forms. Careful thermal regulation thus allowsone to vary the shape of any portions 12 of sheet 12 in a continuousmanner.

The overall structure of sheet 12 where heating elements 14 are mounteddirectly on sheet 12 with only layer 16 interposed between them is verysimple. The assembly process is straightforward and low-cost.

Another embodiment of the invention is shown in FIG. 6. Here atwo-dimensional sheet 26 of SMA material is placed on a coating layer28. In this case, layer 28 is sufficiently thick to provide mechanicalstability during processing.

A thin insulating layer 30 is positioned on top of sheet 26 to provideelectrical insulation between heating elements 14 and sheet 26. Layer 30is thin enough and has appropriate thermal properties to permit the freeflow of heat from elements 14 to sheet 26. Additionally, layer 30 isalso able to accommodate mechanical strains incurred during operation.In this embodiment the SMA material of sheet 26 is also electricallyconducting (e.g., TiNi alloy or CuZnAl alloy).

FIG. 7 showns an embodiment where sheet 26 includes a coating layer andacts as a substrate. In this case layer 28 is chosen from materialswhich are chemically inert and stable to protect sheet 26 from adverseenvironmental conditions.

Electrical insulation between heating elements 32 and sheet 26 isprovided by electrical insulation sections 34 that are depositedpoint-wise under elements 32. Such structures can be produced byinitially applying a layer of insulating material and a layer ofresistive material. Elements 32 and a corresponding electricalinsulation sections 34 are fashioned by dry or wet aetching or anotherwell-known processes.

FIG. 8 shows yet another embodiment in which a two-dimensional sheet 36is made up of an electrically insulating SMA material. In thisconfiguration no insulation is necessary. Consequently, heating elements32 are mounted directly on sheet 36. A coating layer 38 functioning assubstrate is once again provided to afford mechanical stability andresistance to adverse environmental conditions. It is preferable thatlayer 38 also be a good thermal conductor to aid in the dissipation ofheat from sheet 36.

The embodiments of FIGS. 6-8 all operate in the manner set forth above.The modifications introduced are intended to aid one skilled in the artin selecting the appropriate structure given a set of technicalrequirements.

One embodiment of the invention is shown in FIG. 9. A two-dimensionalsheet 40 of an electrically conducting SMA material, preferably a NiTialloy is coated with insulating layer 42. Preferably, layer 42 is madeof Si_(x) N_(y) or polyimide and is sufficiently thin to readily conductheat.

Patterned heating elements 44 are located on layer 42. Elements 44 areobtained by sputtering and patterning TiW or TaO on top of layer 42.Heating elements 44 offer resistance of about a few hundred ohms. In thepreferred embodiment elements 44 have a zig-zag shape when activated.This enables them to ensure better heat distribution in sheet 40 whenactive.

A second insulating layer 46 is provided on top of elements 44 and layer42. Preferably, layer 46 is made of a flexible electrical insulationsuch as polyimide or an elastomer which may be spun coated onto elements44 and layer 42. A number of through-holes 48 are opened in layer 46 topermit electrical contact with elements 44. Holes 48 are aligned withthe terminal portions of elements 44.

A set of conductive paths 50 are patterned on top of layer 46. In oneembodiment, conductive paths 50 are configured to deliver current to aselected portion of sheet 12 and provide ohmic heating to the selectedportion of sheet 12. In another embodiment the ground return path issheet 12 itself. Preferably, conduction lines 50 are made of a flexibleand highly conductive material such as gold. Lines 50 can be defined bypatterning or other suitable techniques. A common return line 50A islaid out to provide electrical contact with the left terminals of allelements 44. Return line 50A saves surface area of top of layer 46 andis desirable as long as all elements 44 are not addressed simultaneouslyon a continuous basis. If continuous activation is required, then anadditional full width layer would be dedicated for the return path.Alternatively, conductive sheet 40 may itself provide the common groundreturn path for all heating elements 44. The other lines, 50B-50E are inelectrical contact with the right terminals of elements 44 respectively.

External electrical connections are made to contact pads 52A-52E,corresponding to lines 50A-50E. For this purpose, pads 52A-52E are muchthicker than lines 50A-50E. The actual electric connections are madewith wire bonding or similar means.

Once the entire structure on sheet 40 is assembled, the SMA is "trained"by forcing sheet 40 to assume a resultant shape using well-knownmethods. For example, sheet 40 is formed on a mandrel and fixed in placewith a clamp. The entire fixture is then placed in an annealing furnace,preferably purged with an inert gas, at approximately 450 degrees C. forabout 30 minutes. Upon cooling the film is released from the mandrel. Atthis time sheet 40 is operationally ready.

The electrical diagram showing the electrical connections of oneembodiment is found in FIG. 10. A control unit 54 is connected to acurrent supply 56. Preferably, both unit 54 and supply 56 are locatedaway from sheet 40. Unit 54 is preferably a micro-processor capable ofselecting a desired combination of elements 44. Current supply 56 ispreferably an adjustable source capable of delivering current to theselected combination of elements 44. Lines 50A-50E are connecteddirectly to supply 56. Elements 44A-44D are shown as resistors. Returnline 50A is grounded.

During operation control unit 54 selects a combination of elements 44 tobe activated. It then sends a corresponding command to supply 56. Supply56 responds by delivering current to elements 44 of the chosencombination. For example, elements 44A and 44D are chosen. Current isdelivered to elements 44A and 44D and the corresponding adjacentportions 58A and 58D assume a well-defined shape. If the current issufficiently large and the temperature maintained in adjacent portions58A and 58D is above T₂ (see FIG. 5) then portions 58A and 58D willassume their pre-trained shape. If the temperature is between T₁ and T₂portions 58A and 58D will assume an intermediate shape which isdependent on the path of travel about the hysterisis loop of FIG. 5.Because supply 56 is adjustable the proper current can be selectedduring operation and adjusted on an empirical basis. Consequently, theshape of portions 58A and 58D can be varied as necessary.

FIG. 11 illustrates the resultant shape of sheet 40 when adjacentportions 58C and 58D are selected. It is assumed that the SMA waspre-trained to curve upward along its entire length. Thus, together,deflections in portions 58C and 58D contribute to a much larger totaldeflection. FIG. 12 illustrates another possible resultant shape oflayer 40 when sections 58B-58D are heated and the SMA was pre-trained toassume an S-shape. Throughout the description it is understood that theSMA of sheet 40 can be trained before or after assembly. Training beforeassembly can be preferable when working with materials which would bedamaged if trained together with the SMA, e.g., due to the highannealing temperatures.

In another embodiment, sheet 40 has a coating layer 60 as shown in FIG.14. For better understanding, the deflections in sheet 40 have beenindicated. Deflection sensors 62 are positioned on layer 60. Sensors 62can be either angular deflections sensors, extension deflection sensorssuch as a strain gage, or bend sensors. A bend sensor is a type ofstrain gage configured for measuring bending strain and angulardeflection. In this case sensors 62 have been placed in locationscorresponding to those of elements 44. Depending on the geometry andapplication, different placement may be preferable.

The electrical diagram with sensors 62 is shown in FIG. 13. The dottedline represents elements mounted on sheet 40. While the connections toelements 44A-44D remain the same, all sensors 62A-62D are wired tocontrol unit 54 via lines 64A-64D respectively. In this manner unit 54can receive signals representative of the local deflection from each oneof sensors 62A-62D individually. A path shape library 66 is connected tocontrol unit 54. Path shape library 66 is capable of mapping theresultant shape of sheet 40 based on information delivered from sensors62.

Preferably, path shape library 66 has an inventory of resultant shapesproduced by known combinations of elements 44. In other words, pathshape library 66 is capable of recalling mapped resultant shapespositions and storing new ones. In the most preferred embodiment pathshape library 66 can also store the actual current values correspondingto intermediate shapes of adjacent portions. This means that inoperation shapes can be recalled and stored at will. The embodiment isthus highly versatile and practical for any diverse applications, e.g.,guiding catheters.

FIG. 15 shows another embodiment which differs from the above only inthat sensors 62 are positioned between elements 44. FIG. 16 showsanother modification in which a temperature sensor 68 is mounted betweenelements 44. This is advantageous for monitoring the temperature ofsheet 40. In a particularly preferred embodiment this data is stored inpath shape library 66. Checking the temperature form sensor 68 duringoperation can prevent overheating and other related malfunctions. Ofcourse, more than one thermal sensor 68 can be provided. Ideally, anumber of such sensors 68 can be provided. Ideally, a number of suchsensors 68 are optimally positioned on sheet 40.

FIG. 17 shows the embodiment of FIG. 14 in the martensitic stateencapsulated in a top coating layer 70. Layer 70 is applied to protectthe electrical connections and elements 44 in particular from damagingenvironmental factors, e.g., corrosive environments.

FIG. 18 and FIG. 19 show two ways in which a two-dimensional sheet 72 ofSMA can be cooled. For simplicity, all other elements, except forheating elements 76, have been omitted. In FIG. 18 the cooling elementis a set of fins 78 in direct contact with sheet 72. This arrangementensures efficient heat transfer and dissipation. Similarly, thestructure id FIG. 19 efficiently dissipates heat using a substrate layer80 with ducts 82 (only one shown). Ducts 82 carry a coolant, e.g.,water, which absorbs and carries away the waste thermal energy.

As shown in FIG. 20, a two way shape memory effect of sheet 12 is shownwith sheet 12 (hereafter "actuator 12") positioned coincident along acatheter 84 axis. Actuator 12 can be made of a shape memory material ora bimorph structure and can formed of a continuous sheet, adiscontinuous sheet, a rod, mesh, wire-like structure as well as otherthree dimensional shapes. It will be appreciated that actuator 12 canalso be parallel but adjacent to the catheter axis, as well aspositioned on a surface of catheter 84. The two-way shaped memory effectprovides for a deflection in two directions and a portion of actuator 12is strained which provides an internal bias spring force. Actuator 12then bends one way in its activated state and returns to the oppositedirection in its inactivated state. Only a portion of actuator 12 canhave a two-way shape.

Referring now to FIG. 21, two single SMA actuators 12 are illustrated.Each actuator 12 operates in a one way shape memory effect. The twoactuators 12 are mechanically coupled and thermally insulated from oneanother. The use of two single actuators 12 in this manner can be usedas a stand along guide wire or as a component of a catheter of othermedical where guidance is needed.

As illustrated in FIG. 22, actuator 12 is coupled to catheter 84. Aplurality of segments 12' are formed from a single actuator 12 and arepositioned in an interior of catheter 84, at an exterior surface ofcatheter 84, or are formed within a catheter body. Additionally,actuator 12 can be a guide wire used with catheter 84.

Actuation of actuator 12 can be in a push or pull mode. The push mode isshown in FIG. 23. If actuator 12 is pushed then an outer jacket is notrequired. If actuator 12 is pulled, an outer jacket is required. Theouter jacket provides thermal insulation and coupling where actuator 12has a plurality of sections which can be "finger-like segments". Whencatheter 84 is formed of any material that provides slippage ordeformation, and actuator 12 is coupled to such a catheter 84, then asleeve that provides a low coefficient of friction of actuator 12 withrespect to catheter 84, is not required.

In FIG. 24(a), actuator 12 is positioned at a distal end of catheter 84.Actuator 12 includes a plurality of finger-like segments that areseparated by slots 85 that extend to the distal end of actuator 12. Inthe embodiment of FIG. 24(a), catheter 84 does not include a core andonly a single continuous actuator 12 is provided. The distal end ofcatheter 84 is capable of attaining complex shapes and bends in multipleplanes by selectively applying energy to different sections of actuator12. In the embodiment illustrated in FIG. 24, actuator 12 includes aproximal end that is joined to catheter 84 by methods well known tothose skilled in the art. As shown in FIG. 24(b) the distal ends of thefinger-like segments of actuator 12 are joined to the distal end ofcatheter 84.

Slots 85 in FIGS. 24(a), (b) and (c) are spaced sufficiently close suchthat the combined maximum lateral and normal surface strain at eachfinger-like segment does not exceed 10% during lateral bending, andpreferably does not exceed 5%. Slots 85 are sufficiently narrow tomaximize bending forces of the finger-like segments while permittinglateral strain.

Referring now to FIG. 24(c) actuator 12 includes a plurality of slots 85which do not extend to the proximal or distal ends of actuator 12. Inthis embodiment, a separate coupling element is not needed.

In FIG. 25, actuator 12 is shown as being positioned in an interior ofcatheter 84 without an additional coupling device or a core positionedin catheter 84. As illustrated in FIG. 26, actuator 12 is positioned ina body of catheter 84 and may be co-extruded.

Referring now to FIG. 27, only selected sections of actuator 12 arelocally heated by selected heating elements and the proximity of heatingelements 14 to actuator 12 provide a thermal path whereby energy istransferred by heating elements 14 to one or more sections of actuator12. Upon activation a section of actuator 12 moves partially of fully toits minimum bend radius imparted to it during its thermal training. InFIG. 28, actuator 12 is shown as being positioned in a lumen-lesscatheter 84.

As shown in FIG. 29, actuator 12 is a shape memory alloy mesh instead ofa solid sheet. In FIG. 30 the mesh configuration is formed in a basketand thermally trained in a crushed configuration. The mesh can beco-extruded with an elastomer 86 which can be the catheter 84 or aseparate element. Elastomer 86 can also be cast, heat shrunk, dipped andthe like with mesh 12. Elastomer 86 provides the function of a returnspring to the one-way action of actuator 12. The one-way springactuation can also be provided by other mechanical devices, structureand configurations. Thin film heaters 14 are distributed on surfaces ofthe mesh and provide local heating of the shape memory alloy mesh 12. InFIG. 31, different sections of mesh 12 are activated to varying degreesin order to achieve a desired deflection the elastomer.

Referring now to FIG. 32, actuator 12 is a shape memory alloy corrugatedtube 12 which provides for large axial contractions. The shape memoryalloy corrugated tube 12 can be co-extruded with elastomer 86 which canbe the catheter 84 or a separate element. Thin film heater elements 14are positioned on a surface of the shape memory alloy corrugated tube 12and provide local heating of the shape memory corrugated tube. In FIG.33, different sections of the shape memory alloy corrugated tube 12 areactivated to varying degrees in order to achieve a desired deflection ofthe elastomer 86. Referring now to FIG. 34, a cross-sectional view ofshape memory alloy corrugated tube 12 is illustrated. Heating elements14 are positioned on the surface of shape memory alloy corrugated tube12 and a return spring function is provided by elastomer 86 which can beinside, outside or co-extruded with shape memory alloy corrugated tube12. Additionally, the return spring function can be provide a superelastic form of shape memory alloy sheet 12 which is mechanicallycoupled to shape memory alloy corrugated tube 12.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. For example, a Peatier device could alsoprovide an equivalent solution to heat dissipation. Therefore, personsof ordinary skill in this field are to understand that all suchequivalent structures are to be included within the scope of thefollowing claims.

What is claimed is:
 1. A catheter, comprising:an elongated deviceincluding a distal end, a proximal end, and a longitudinal axis; a shapememory alloy member coupled to the elongated device; an insulating filmpositioned on a surface of the shape memory alloy member andelectrically isolating the shape memory alloy member from passage ofcurrent through the shape memory alloy member; and a plurality ofindependently controllable heating elements patterned on the insulatingfilm, each of the independently controllable heating elements of theplurality providing heat to an adjacent selected section of the shapememory alloy member and providing activation of only an area below theindependently controllable heating element of the elongated device in alateral direction relative to the longitudinal axis of the elongatedmember.
 2. The catheter of claim 1, wherein an activation of at least aportion of the selected section provides a variable Young's modulus ofat least a portion of the shape memory alloy member.
 3. The catheter ofclaim 1, further comprising: a micro-fabricated conductive path coupledto the plurality of independently controllable heating elements.
 4. Thecatheter of claim 1, wherein the member is positioned substantiallyparallel to the longitudinal axis of the elongated device.
 5. Thecatheter of claim 1, wherein the member is a continuous sheet.
 6. Thedevice of claim 1, wherein the member is a sheet which includesperforations.
 7. The catheter of claim 1, wherein the shape memory alloymember is made of a plurality of interconnected separate shape memoryalloy members.
 8. The catheter of claim 1, wherein the shape memoryalloy member has a three-dimensional geometry.
 9. The device of claim 1,wherein the member is a wire-like structure.
 10. The catheter of claim1, wherein the shape memory alloy member is a tube-like structure.
 11. Acatheter, comprising:an elongated device including a distal end, aproximal end, and a longitudinal axis; a shape memory alloy membercoupled to the elongated device; an insulating film positioned on asurface of the shape memory alloy member and electrically isolating theshape memory alloy member from passage of current through the shapememory alloy member; and a plurality of independently controllableheating elements patterned on the insulating film, each of theindependently controllable heating elements of the plurality providingheat to an adjacent selected section of the shape memory alloy memberand providing activation of only an area below the independentlycontrollable heating element of the elongated device in a lateraldirection relative to the longitudinal axis of the elongated member,wherein the shape memory alloy member includes at least one slot formedin the shape memory alloy member.
 12. The catheter of claim 1, whereinthe member is positioned on an external surface of the elongated device.13. The catheter of claim 1, wherein the shape memory alloy member ispositioned on an internal surface of the elongated device.
 14. Thecatheter of claim 1, wherein the member is positioned on an externalsurface of the elongated device.
 15. The catheter of claim 1, whereinthe shape memory alloy member is positioned in an interior section ofthe elongated device.
 16. The catheter of claim 1, wherein the member ispositioned at least partially circumferentially around the elongateddevice.
 17. The catheter of claim 1, wherein the member is positioned atleast partially circumferentially at an exterior surface of theelongated device.
 18. The catheter of claim 1, wherein the shape memoryalloy member is positioned at least partially circumferentially at aninterior surface of the elongated device.
 19. The catheter of claim 1,wherein the shape memory alloy member is positioned at least partiallycircumferentially in an interior of the elongated device.
 20. Thecatheter of claim 1, wherein the elongated device has a tubulargeometric configuration.
 21. The catheter of claim 1, wherein theelongated device has a solid cross-section.
 22. The catheter of claim 1,wherein the elongated device includes an interior lumen.
 23. A catheter,comprising: a shape memory alloy member with a longitudinal axis andconfigured to be selectively activated at a selected site of the shapememory alloy member;an insulating film positioned on a surface of theshape memory alloy member and electrically isolating the shape memoryalloy member from passage of current through the shape memory alloymember; and a plurality of independently controllable heating elementspatterned on the insulating film, each of the independently controllableheating elements of the plurality providing heat to an adjacent selectedsection of the shape memory alloy member and providing activation ofonly an area below the independently controllable heating element of theadjacent selected section in a lateral direction relative to thelongitudinal axis of the sheet of the shape memory alloy member.
 24. Thecatheter of claim 23, wherein an activation of at least a portion of theselected section provides a variable Young's modulus of at least aportion of the shape memory alloy member.
 25. The catheter of claim 23,further comprising:a micro-fabricated conductive path coupled to theplurality of independently controllable heating elements.
 26. Acatheter, comprising: a shape memory alloy member with a longitudinalaxis and configured to be selectively activated at a selected site ofthe shape memory alloy member;an insulating film positioned on a surfaceof the shape memory alloy member and electrically isolating the shapememory alloy member from passage of current through the shape memoryalloy member; and a plurality of independently controllable heatingelements patterned on the insulating film, each of the independentlycontrollable heating elements of the plurality providing heat to anadjacent selected section of the shape memory alloy member and providingactivation of only an area below the independently controllable heatingelement of the adjacent selected section in a lateral direction relativeto the longitudinal axis of the sheet of the shape memory alloy member;and a plurality of patterned conductor lines, each of the patternedconductor lines being coupled to an independently controllable heatingelement, the plurality of conductor lines being patterned on theinsulating film.
 27. The catheter of claim 23, wherein the shape memoryalloy member is made of a plurality of interconnected separate shapememory alloy members.
 28. The catheter of claim 23, wherein the shapememory alloy member includes at least one slot formed in the shapememory alloy member.
 29. A catheter, comprising:an elongated deviceincluding a distal end, a proximal end, and a longitudinal axis; a shapememory alloy member coupled to the elongated device; an insulating filmpositioned on a surface of the shape memory alloy member andelectrically isolating the shape memory alloy member from passage ofcurrent through the shape memory alloy member; and a plurality ofindependently controllable heating elements patterned on the insulatingfilm, each of the independently controllable heating elements of theplurality providing heat to an adjacent selected section of the shapememory alloy member and providing activation of only an area below theindependently controllable heating element of the elongated device in alateral direction relative to the longitudinal axis of the elongatedmember; and a plurality of conductor lines, each of the conductor linesbeing coupled to an independently controllable heating element, theplurality of conductor lines being patterned on the insulating film.